1. Field of the Invention
The present invention relates to an liquid crystal display(LCD), and more particularly to a LCD having an ohmic layer made of an amorphous diamond.
2. Related Art
Thin film transistors (TFTs) generally used as a switching device, are classified into a staggered type, an inverse staggered type and a coplanar type. The staggered type and the inverse staggered type have a gate electrode below which an active layer is formed and a source electrode and a drain electrode formed on the active layer. The coplanar type TFT has a gate electrode and a source electrode and a drain electrode which all are formed on an active layer. The active layer ohmic layer is made from an amorphous silicon, poly silicon or compound such as CdSe. Among them, a TFT using hydrogenated amorphous silicon has a benefit in respect to a production yield and a large area, so the hydrogenated amorphous silicon is widely employed in the active layer and the ohmic layer.
Since the hydrogenated amorphous silicon(a-Si:H) has a low electric field mobility and a high optical-electrical conductivity, that is, a-Si:H is unstable in light and in an electric field, the hydrogenated amorphous silicon TFT has a large leakage current. Also, since the ohmic layer composed of the hydrogenated amorphous silicon has low conductivity, the a-Si:H TFT has a low on-current and a high off-current.
On the other hand, for reducing the leakage current, methods have been proposed for manufacturing a self-aligned or completely self-aligned a-Si:H TFT or for reducing the thickness of the a-Si:H layer. The completely self-aligned a-Si:H TFT has low electric field mobility, and the process for reducing the thickness of the a-Si:H layer is practically difficult.
Accordingly, there is a need for a TFT improving an on-current feature and reducing a leakage current, without reducing the thickness of the ohmic layer and forming a self-aligned a-Si:H TFT.